Oil pressure drops on acceleration

[mtbinscotland]

The oil pressure on my 91 Legend is fine at idle but drops significantly on full acceleration then recovers at about 20 mph.  Oil level is fine and there are no visible leaks.  Any advice?  Has anybody's oil pressure switch/sender failed and needed replacing?  Also, I'm in the UK, so not sure if there is a suitable replacement part for this over here but if anyone can recommend what part I should look for, I'd be grateful!
Thanks, as always...

[mtbinscotland]

http://www.europaspares.com/oil-pressure-sender-unit-oil-pressure-sender-unit-1-8-nptf.html

I've been searching a bit online .  Will this work?

[mtbinscotland]

Oh and here is the actual unit in  my 91 legend.
Cheers

[shyskier]

Looks like that sending unit will work. It is best to check pressure with a gage installed on engine,they are fairly cheap, or borrow from a mechanic, or parts store if they loan tools.
Sending unit is cheap but do not chance running with low pressure.

[mtbinscotland]

Thanks shyskier.
What should the ideal psi be at idle, at 3000 rpm and then at full acceleration?
On second look, oil looks quite dark in colour...I guess no should also perform an oil and filter change while I'm at it?
Cheers

[shyskier]

I'm not sure of exact spec. but over 25 psi should be o.k. My 88 5.7L runs 40psi with engine warm.

[backfoot100]

Oil pressure should be about 40PSI warmed up and idling but certainly not concrete. Then they say 10 additional PSI/1000RPM although I've never trusted that. Mine runs about 25-30PSI warmed and up to 70-80PSI WOT. Oil pressure can change depending on what weight oil you run too.

Usually a drop in pressure is indicative of a low oil level but you say it's OK. I'm not sure why you would be getting what you are getting. Shyskier is right in that verifying oil pressure with a mechanical gauge would be my first task. They're pretty cheap or you might even be able to borrow one from a shop. You can plumb that right in with the existing sender.

Be careful of that sender you posted. The ohm value of the sender needs to match the ohm value of the gauge. I'm pretty sure that these gauges were all 33-240 ohm so the sender has to match. Ron would probably have to verify the correct gauge. You could also crawl under the dash and look at the back side of the gauge. It may say what the ohm value is.